Power amplifier with output harmonic resonators

ABSTRACT

Embodiments of circuits and systems for a radio frequency (RF) power amplifier employing output harmonic resonators are disclosed. The RF power amplifiers may include amplification circuitry having unit cells and output harmonic resonators co-disposed on a chip. In some embodiments, each unit cell may be coupled with a respective output harmonic resonator. Other embodiments may be described and claimed.

FIELD

Embodiments of the present disclosure relate generally to the field ofcircuits, and more particularly to a power amplifier with outputharmonic resonators.

BACKGROUND

Radio frequency (RF) power amplifiers are used in wireless transmissiondevices to amplify an RF signal for transmission. Power consumption is aconcern for users and manufacturers of these wireless transmissiondevices. One of the factors in determining the power consumption in suchdevices is the direct current (DC)-to-RF conversion efficiency of the RFpower amplifiers. DC-to-RF conversion efficiency may be a measure of howmuch DC power is converted into RF energy.

High DC-to-RF conversion efficiencies have been demonstrated at aunit-cell level. However, when RF power amplifiers employ multiple unitcells, efficiency degrades due to these devices failing to providedesired impedance matching across fundamental and harmonic operatingfrequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 illustrates a wireless device in accordance with variousembodiments.

FIG. 2 illustrates amplification circuitry of an RF power amplifier inaccordance with various embodiments.

FIG. 3 illustrates an output harmonic resonator in accordance withvarious embodiments.

FIG. 4 illustrates Smith chart impedance plots in accordance withvarious embodiments.

FIG. 5 illustrates a circuit including an input harmonic resonator, aunit cell, and an output harmonic resonator in accordance with variousembodiments.

FIG. 6 illustrates layouts of internal harmonic tuned unit cells inaccordance with various embodiments.

FIG. 7 illustrates an output harmonic resonator in accordance withvarious embodiments.

FIG. 8 illustrates an internally-tuned unit cell circuit in accordancewith various embodiments.

FIG. 9 is a flowchart illustrating operation of an amplification circuitin accordance with various embodiments.

DETAILED DESCRIPTION

Various aspects of the illustrative embodiments will be described usingterms commonly employed by those skilled in the art to convey thesubstance of their work to others skilled in the art. However, it willbe apparent to those skilled in the art that alternate embodiments maybe practiced with only some of the described aspects. For purposes ofexplanation, specific devices and configurations are set forth in orderto provide a thorough understanding of the illustrative embodiments.However, it will be apparent to one skilled in the art that alternateembodiments may be practiced without the specific details. In otherinstances, well-known features are omitted or simplified in order not toobscure the illustrative embodiments.

Further, various operations will be described as multiple discreteoperations, in turn, in a manner that is most helpful in understandingthe present disclosure; however, the order of description should not beconstrued as to imply that these operations are necessarily orderdependent. In particular, these operations need not be performed in theorder of presentation.

The phrase “in one embodiment” is used repeatedly. The phrase generallydoes not refer to the same embodiment; however, it may. The terms“comprising,” “having,” and “including” are synonymous, unless thecontext dictates otherwise.

In providing some clarifying context to language that may be used inconnection with various embodiments, the phrases “A/B” and “A and/or B”mean (A), (B), or (A and B); and the phrase “A, B, and/or C” means (A),(B), (C), (A and B), (A and C), (B and C) or (A, B and C).

As used herein, “coupled with” may mean either one or both of thefollowing: a direct coupling or connection, where there is no otherelement coupled or connected between the elements that are said to becoupled with each other; or an indirect coupling or connection, whereone or more other elements are coupled or connected between the elementsthat are said to be coupled with each other.

FIG. 1 illustrates a wireless transmission device 100 in accordance withvarious embodiments. The wireless transmission device 100 may have anantenna structure 104, a duplexer 108, a transmitter 112, a receiver116, transmit/receive (TX/RX) circuitry 120, a main processor 124, and amemory 128 coupled with each other at least as shown. While the wirelesstransmission device 100 is shown with transmitting and receivingcapabilities, other embodiments may include wireless transmissiondevices without receiving capabilities.

In various embodiments, the wireless transmission device 100 may be, butis not limited to, a mobile telephone, a paging device, a personaldigital assistant, a text-messaging device, a portable computer, a basestation, a radar, a satellite communication device, or any other devicecapable of wirelessly transmitting RF signals.

The main processor 124 may execute a basic operating system program,stored in the memory 128, in order to control the overall operation ofthe wireless transmission device 100. For example, the main processor124 may control the reception of signals and the transmission of signalsby TX/RX circuitry 120, receiver 116, and transmitter 112. The mainprocessor 124 may be capable of executing other processes and programsresident in the memory 128 and may move data into or out of memory 128,as desired by an executing process.

The TX/RX circuitry 120 may receive outgoing data (e.g., voice data, webdata, e-mail, signaling data, etc.) from the main processor 124. TheTX/RX circuitry 120 may transmit an RF signal that represents theoutgoing data to the transmitter 112. The transmitter 112 may include anRF power amplifier 132 (hereinafter also referred to as “RF amplifier132”) to amplify the RF signal for transmission. The amplified RF signalmay be forwarded to the duplexer 108 and then to the antenna structure104 for an over-the-air (OTA) transmission.

In a similar manner, the TX/RX circuitry 120 may receive an incoming OTAsignal from the antenna structure 104 through the duplexer 108 andreceiver 116. The TX/RX circuitry 120 may process and send the incomingsignal to the main processor 124 for further processing.

In various embodiments, the antenna structure 104 may include one ormore directional and/or omnidirectional antennas, including, e.g., adipole antenna, a monopole antenna, a patch antenna, a loop antenna, amicrostrip antenna or any other type of antenna suitable for OTAtransmission/reception of RF signals.

Those skilled in the art will recognize that the wireless transmissiondevice 100 is given by way of example and that, for simplicity andclarity, only so much of the construction and operation of the wirelesstransmission device 100 as is necessary for an understanding of theembodiments is shown and described. In addition, or as an alternative,although an exemplary wireless transmission device 100 is shown anddescribed, various embodiments contemplate any suitable component orcombination of components performing any suitable tasks in associationwith wireless transmission device 100, according to particular needs.Moreover, it is understood that the wireless transmission device 100should not be construed to limit the types of devices in whichembodiments may be implemented.

In accordance with various embodiments, the RF amplifier 132 includesoutput harmonic resonators to facilitate amplification of the RF signalwith a high DC-to-RF conversion efficiency. Various embodiments of theRF amplifier 132, its components, and their operation are described ingreater detail with respect to FIGS. 2-9.

FIG. 2 illustrates amplification circuitry 200 of the RF amplifier 132in accordance with various embodiments. The amplification circuitry 200may include a number of unit cells 204 connected in parallel with oneanother as shown. The unit cells 204 may each have multiple gatefingers. The number and width of the gate fingers may be selected basedon a desired operating frequency.

Each of the unit cells 204 may be coupled with a respective inputharmonic resonator 208 and a respective output harmonic resonator 212.In particular, the input harmonic resonators 208 may be coupled withrespective gate terminals of the unit cells 204, while the outputharmonic resonators 208 may be coupled with respective drain terminalsof the unit cells 204. The unit cells 204 may have their sourceterminals coupled to a ground.

The amplification circuitry 200 may receive an RF signal from an inputmatch circuit 216, amplify the RF signal, and provide the amplified RFsignal to an output match circuit 220. The input match circuit 216 maytransform a source impedance at a fundamental frequency of the RF signalto an impedance that substantially matches the input impedance of theamplification circuitry 200. In a similar manner, the output matchcircuit 220 may transform a load impedance at the fundamental frequencyto an impedance that substantially matches the output impedance of theamplification circuitry 200.

The input and output impedance of the amplification circuitry 200 willbe substantially lower than that of an individual unit cell 204 when anumber of unit cells are coupled in parallel to achieve a high outputpower. This may make it difficult to provide desired harmonic impedanceterminations at the input match circuit 216 and the output match circuit220.

Accordingly, an input harmonic resonator 208 and/or an output harmonicresonator 212 may be provided for each unit cell 204 to facilitateharmonic tuning at the unit-cell level. Harmonic tuning may refer to atuning of the input impedance at the input of the unit cell 204 and/or atuning of the output impedance at the output of the unit cell 204 acrossharmonic frequencies. The higher input/output impedances at theunit-cell level, and in particular the higher fundamental impedance thatresults in a higher fundamentaltoharmonic impedance ratio, mayfacilitate this harmonic tuning. This may result in a higher DC-to-RFconversion efficiency of the RF amplifier 132 than would otherwiseresult from using the input match circuit 216 and/or output matchcircuit 220 for harmonic tuning.

In some embodiments, the input harmonic resonators 208 and/or the outputharmonic resonators 212 may be internal resonators. An internalresonator, as used herein, may refer to a resonator that is formed onthe same chip as the unit cell 204 with which it is coupled. Harmonictuning from internal resonators on a unit-cell level may provide the RFamplifier 132 with desired linear and high-efficiency operation over alarger range of operating frequencies than what is currently provided byexternal resonators that are coupled to multiple unit cells.

The unit cells 204, and any internal resonators, may be formed on agallium arsenide (GaAs) chip. However, other embodiments may use chipsincluding other semiconductor materials, e.g., silicon, indiumphosphide, silicon carbide, etc.

In some embodiments, the unit cells 204 may be field-effect transistors,e.g., heterostructure field-effect transistors (HFETs),metal-semiconductor field effect transistors (MESFETs), high electronmobility transistors (HEMTs) (e.g., GaAs pseudomorphic HEMTs, aluminumgallium nitride (AlGaN)/GaN HMETs and all their derivatives, etc.), etc.Other embodiments may use other transistor technologies such as, but notlimited to, bipolar junction transistor (BJT) technology, e.g.,heterojunction bipolar transistors (HBTs).

FIG. 3 illustrates an output harmonic resonator 300 in accordance withvarious embodiments. The output harmonic resonator 300 may be similarto, and interchangeable with, the output harmonic resonators 212.

The output harmonic resonator 300 may include a capacitor 304 coupled inparallel with an inductor 308. The output harmonic resonator 300 mayalso include an inductor 312 coupled in series with the capacitor 304and inductor 308.

The output harmonic resonator 300 may be coupled with a ground through acapacitor 316 that may function as a bypass capacitor. A drain bias maybe provided at a node 320 between the output harmonic resonator 300 andthe capacitor 316.

The output impedance at the drain terminal of a unit cell may berepresented by a capacitor 324 coupled in parallel with a resistor 328.The unit cell output capacitance and resistance values may depend on thetransistor technology that is employed, the size of the transistor,and/or the device layout. As can be seen from the illustrated boundaryof the output harmonic resonator 300, the unit cell output capacitance,modeled by the capacitor 324, may be absorbed into the output harmonicresonator 300.

The components of the output harmonic resonator 300 may be co-located ona chip with a unit cell by using metal-insulator-metal (MIM) capacitorsand spiral inductors implemented through conventional microwavemonolithic integrated circuit (MMIC) processing techniques. Known designequations may be employed to calculate the values desired from thecomponents of the output harmonic resonator 300.

Through operation, the output harmonic resonator 300 may create a seriesand/or parallel resonance at the harmonic frequencies of the unit cellcoupled with the output harmonic resonator 300. For example, the outputharmonic resonator 300 may create a parallel resonance at a thirdharmonic frequency, resulting in a relatively high impedance. The outputharmonic resonator 300 may also create, for example, a series resonanceat a second harmonic frequency, resulting in a relatively low impedance.Thus, the output harmonic resonator 300 may facilitate provision ofdesired impedances for matching the impedance of the unit cells acrossvarious harmonic frequencies, for high-efficiency and linear operationsof the RF amplifier 132.

This relationship of the operating frequency to the output impedance ofa GaAs pHEMT, for example, is shown by Smith chart impedance plots ofFIG. 4 in accordance with some embodiments. In particular, plots 404 and408 show output impedance corresponding to a fundamental frequency of3.5 gigahertz (GHz), a second harmonic frequency of 7 GHz, and a thirdharmonic frequency of 10.5 GHz for two different harmonically-tuned unitcells. Plot 404 shows output impedance provided by an output harmonicresonator for a unit cell having sixteen gate fingers, each gate fingerhaving a width of two-hundred fifty microns (μm). A unit cell with theseproperties may also be referred to as 16×250 μm unit cell. The plot 408shows output impedance provided by an output harmonic resonator for a4×250 μm unit cell. As can be seen by the plots in this example, theoutput harmonic resonators may provide a series resonance withrelatively low output impedance at the second harmonic frequency, whileproviding parallel resonance with relatively high output impedance atthe third harmonic frequency.

FIG. 5 illustrates a circuit 500 including the unit cell 204 coupledwith an input harmonic resonator 504 and the output harmonic resonator300 in accordance with various embodiments. In particular, the inputharmonic resonator 504 may be coupled with a gate terminal of the unitcell 204 and go to a relative ground. The input harmonic resonator 504may include an inductor 508 coupled in series with a capacitor 512. Theinductor 508 may have a first terminal coupled with the gate terminal ofthe unit cell 204 and a second terminal coupled with the capacitor 512.The input harmonic resonator 504 may provide a series resonance at thesecond harmonic frequency of the unit cell 204 to provide a shortcircuit and a correspondingly low impedance as seen from the gateterminal of the unit cell 204.

FIGS. 6( a)-6(b) illustrate layouts of internal harmonic tuned unitcells in accordance with various embodiments. In particular, internalharmonic tuned unit cell 604 of FIG. 6( a) and internal harmonic tunedunit cell 608 of FIG. 6( b) are shown implemented on respective chips.The internal harmonic tuned unit cells 604 and/or 608 may be representedschematically by the circuit 500 in accordance with some embodiments.

The internal harmonic tuned unit cell 604 may include a unit cell 612having a gate terminal 614 coupled with an input harmonic resonator 616and further coupled with each of sixteen gate fingers 618 of the unitcell 612 through an interconnect 620. The unit cell 612 may also have adrain terminal 622 coupled with each of sixteen drain fingers 624through an interconnect 626 and further coupled with an output harmonicresonator 628. The unit cell 612 may be a 16×250 μm unit cell. The inputharmonic resonator 616 may have a spiral inductor 632 coupled in serieswith a capacitor 634. The input harmonic resonator 616 may be coupledbetween the unit cell 612 and a ground through a via 636 to a backsideground plane.

The output harmonic resonator 628 may include a first spiral inductor638 coupled in parallel with a capacitor 640. The output harmonicresonator 628 may also include a second spiral inductor 644 coupled inseries with the first spiral inductor 638 and the capacitor 640. Theoutput harmonic resonator 628 may also be coupled with a bypasscapacitor 648 that is coupled with the backside ground plane throughvias 652.

The internal harmonic tuned unit cell 608 may have components similar tothe internal harmonic tuned unit cell 604, including an input harmonicresonator 656, a unit cell 660, and an output harmonic resonator 664.However, the unit cell 660 may be smaller than the unit cell 612. Forexample, the unit cell 660 may be a 4×250 μm unit cell. The size of thecomponents of the harmonic resonators may be adjusted accordingly. Forexample, spiral inductors used for a 4×250 μm unit cell may be largerthan spiral inductors used for a 16×250 μm unit cell, as is generallyshown in FIG. 6.

FIG. 7 illustrates an output harmonic resonator 700 in accordance withvarious embodiments. The output harmonic resonator 700 may besubstantially interchangeable with the output harmonic resonator 300.The output harmonic resonator 700 may include a capacitor 704 coupled inseries with an inductor 708. The output harmonic resonator 700 may alsoinclude a capacitor 712 coupled in parallel with the capacitor 704 andthe inductor 708.

Similar to the output harmonic resonator 300, the output harmonicresonator 700 may be coupled between a bypass capacitor 716, which goesto a ground, and a drain terminal of a unit cell, modeled by a capacitor720 and resistor 724. The output harmonic resonator 700 may functionsimilar to the output harmonic resonator 300 described above.

An RF amplifier employing the internal resonators described in FIGS. 3-7may be a class F amplifier, which may be a high-efficiency,high-frequency switching power amplifier. However, other embodiments maybe used in other types of amplifiers. For example, FIG. 8 illustrates aninternal harmonic tuned unit cell circuit 800 that may be used in aclass E amplifier in accordance with some embodiments. A class Eamplifier may be another type of a high-efficiency, high-frequencyswitching power amplifier.

The circuit 800, which may be coupled in parallel with other similarcircuits as shown in FIG. 2, includes an input harmonic resonator 804coupled with a gate terminal of a unit cell 204. A drain terminal of theunit cell 204 may be coupled with an output harmonic resonator 808. Theoutput harmonic resonator 808 may be an internal series resonator havingan inductor 812 coupled in series with a capacitor 816. An internalseries resonator may be a resonator that is particularly suitable for aclass E amplifier by being configured, for example, to provide highimpedances at all of the harmonic frequencies for desired operation. Aseries reactance jX, for the fundamental frequency, may be determined bya difference in reactances of the inductor 812 and capacitor 816. Aresistor 820 may represent a load impedance.

The drain terminal of the unit cell 204 may also be coupled with a drainvoltage Vd through an inductor, for example, an iron-core inductor 814.A capacitor 818 may represent an intrinsic output capacitance of theunit cell 204.

The input harmonic resonator 804, which may also be an internal seriesresonator, may include an inductor 824 and a capacitor 828 and operatesimilar to input harmonic resonators described above.

FIG. 9 illustrates a flowchart 900 illustrating operation of anamplification circuit in accordance with various embodiments. At block904, an RF signal may be amplified by a plurality of unit cells. Asshown above, the unit cells may be coupled in parallel with one another.At block 908, an output of each of the plurality of unit cells may beharmonically tuned with a respective output harmonic resonator. Asdiscussed above, the output harmonic resonators may be internalresonators. At block 912, an input of each of the plurality of unitcells may be harmonically tuned with a respective input harmonicresonator. Harmonic tuning of the inputs and/or outputs of the unitcells may be done as described with respect to any of the aforementionedembodiments.

Although the present disclosure has been described in terms of theabove-illustrated embodiments, it will be appreciated by those ofordinary skill in the art that a wide variety of alternate and/orequivalent implementations calculated to achieve the same purposes maybe substituted for the specific embodiments shown and described withoutdeparting from the scope of the present disclosure. Those with skill inthe art will readily appreciate that the teachings of the presentdisclosure may be implemented in a wide variety of embodiments. Thisdescription is intended to be regarded as illustrative instead ofrestrictive.

1. A circuit comprising: a plurality of unit cells, each having an inputto receive a radio frequency (RF) signal and an output to transmit anamplified RF signal; and a plurality of output harmonic resonatorsrespectively coupled with the outputs of the plurality of unit cells toprovide harmonic termination impedances to the outputs of the pluralityof unit cells, wherein each of the plurality of output harmonicresonators comprises a first inductor coupled in parallel with acapacitor and a second inductor coupled in series with the firstinductor and the capacitor.
 2. The circuit of claim 1, wherein theplurality of unit cells and the plurality of output harmonic resonatorsare implemented on a chip.
 3. The circuit of claim 2, furthercomprising: a plurality of input harmonic resonators respectivelycoupled with the inputs of the plurality of unit cells to provideharmonic termination impedances to the inputs of the plurality of unitcells.
 4. The circuit of claim 3, wherein each of the plurality of inputharmonic resonators comprise an inductor coupled in series with acapacitor, the inductor having a first terminal coupled with the inputof the unit cell and a second terminal coupled with the capacitor. 5.The circuit of claim 1, wherein each of the plurality of output harmonicresonators provide a series resonance at a second harmonic frequency ofthe amplified RF signal.
 6. A circuit comprising: a plurality of unitcells disposed on a chip, each having an input to receive a radiofrequency (RF) signal and an output to transmit an amplified RF signal;and one or more output harmonic resonators, disposed on the chip,coupled with outputs of the plurality of unit cells to harmonically tunean output impedance for each of the plurality of unit cells, whereineach of the plurality of output harmonic resonators comprises a firstinductor coupled in parallel with a capacitor, and a second inductorcoupled in series with the first inductor and the capacitor.
 7. Thecircuit of claim 6, wherein the one or more output harmonic resonatorscomprise a plurality of output harmonic resonators that respectivelycorrespond to the plurality of unit cells.
 8. The circuit of claim 6,wherein the one or more output harmonic resonators are configured toprovide a series resonance at the output of each of the plurality ofunit cells at a second harmonic frequency of the RF signal toharmonically tune the output impedances.
 9. The circuit of claim 6,wherein the one or more output harmonic resonators are configured toprovide a parallel resonance at the output of each of the plurality ofunit cells at a third harmonic frequency of the RF signal toharmonically tune the output impedances.
 10. The circuit of claim 6,further comprising: one or more input harmonic resonators, disposed onthe chip, coupled with inputs of the plurality of unit cells toharmonically tune an input impedance for each of the plurality of unitcells.
 11. The circuit of claim 6, wherein each of the one or moreharmonic resonators comprise: a spiral inductor and ametal-insulator-metal (MIM) capacitor.
 12. A system comprising: atransmitter including a radio frequency (RF) power amplifier havingamplification circuitry with a plurality of unit cells, each having aninput to receive an RF signal and an output to transmit an amplified RFsignal, and a plurality of output harmonic resonators respectivelycoupled with the outputs of the plurality of unit cells to provideharmonic termination impedances to the outputs of the plurality of unitcells, wherein each of the plurality of output harmonic resonatorscomprises a first inductor coupled in parallel with a capacitor, and asecond inductor coupled in series with the first inductor and thecapacitor; and an antenna structure coupled with the transmitter andconfigured to facilitate an over-the-air (OTA) transmission of theamplified RF signal.
 13. The system of claim 12, wherein the pluralityof unit cells and the plurality of output harmonic resonators areimplemented on a chip.
 14. The system of claim 12, wherein the RF poweramplifier is a class E amplifier.
 15. The system of claim 12, whereinthe RF power amplifier is a class F amplifier.
 16. A method comprising:amplifying, with a plurality of unit cells, a radio-frequency signal;and harmonically tuning an output of each of the plurality of unit cellswith a respective one of a plurality of output harmonic resonators,wherein each of the plurality of output harmonic resonators comprises afirst inductor coupled in parallel with a capacitor, and a secondinductor coupled in series with the first inductor and the capacitor.17. The method of claim 16, wherein the plurality of unit cells and theplurality of output harmonic resonators are implemented on a chip. 18.The method of claim 16, further comprising: harmonically tuning an inputof each of the plurality of unit cells with a respective one of aplurality of input harmonic resonators.
 19. A circuit comprising: aplurality of unit cells, each having an input to receive a radiofrequency (RF) signal and an output to transmit an amplified RF signal;and a plurality of output harmonic resonators respectively coupled withthe outputs of the plurality of unit cells to provide harmonictermination impedances to the outputs of the plurality of unit cells,wherein each of the plurality of output harmonic resonators comprises afirst capacitor coupled in series with an inductor, and ametal-insulator-metal (MIM) capacitor coupled in parallel with the firstcapacitor and the inductor.
 20. The circuit of claim 19, wherein theplurality of unit cells and the plurality of output harmonic resonatorsare implemented on a chip.
 21. The circuit of claim 19, wherein each ofthe plurality of output harmonic resonators provide a series resonanceat a second harmonic frequency of the amplified RF signal.
 22. Thecircuit of claim 19, wherein the one or more output harmonic resonatorsare configured to provide a parallel resonance at the output of each ofthe plurality of unit cells at a third harmonic frequency of the RFsignal to harmonically tune the output impedances.
 23. The circuit ofclaim 19, wherein each of the one or more harmonic resonators comprise:a spiral inductor and a metal-insulator-metal (MIM) capacitor.